In conventional flexographic printing units, an impression cylinder is fixed to side frames and usually driven by a miter type gear box having bevel gears therein or driven through a gear train of some desired type from the main machine drive of the unit. A plate cylinder adjacent to the impression cylinder is driven by a gear mounted on a journal of the impression cylinder and a gear mounted on the journal of the plate cylinder. An intermediate ink transfer cylinder is then driven by a gear mounted suitably on the plate cylinder shaft and a gear mounted on the journal of the intermediate transfer cylinder. An ink fountain cylinder is then driven by a gear mounted on the intermediate transfer cylinder (ITC) through a gear mounted on the journal of the ink fountain cylinder.
Ink is picked up by the fountain cylinder from an ink fountain or well and transferred to the intermediate transfer cylinder which in turn transfers ink to the plate cylinder. The thickness of the film of ink on the intermediate transfer cylinder is controlled by making the ink fountain cylinder adjustable towards and away from the intermediate transfer cylinder by means of screw mounted knobs and slides to permit the operator to squeeze the ink thickness by adjusting one side or the other or both of the fountain cylinder with respect to the intermediate transfer cylinder. A second adjustment is provided in which both the fountain cylinder and the ITC are then moved as a unit by means of slides, screws and knob units to make contacts with the printing plates mounted on the plate cylinder. One side or the other of this entire unit is permitted to be squeezed with adjusting screws by relative movement with respect to the plate cylinder. Finally, all three of these cylinders are adjustable as a unit through slides, screws and knob units, to make contact with the web to be printed which is supported by the impression cylinder. Here again, an operator can squeeze one side or the other or both in regard to the proximity of the plate and impressions cylinders to regulate the transfer of ink from the printing plates on the plate cylinder to the web to be printed.
During this conventional set up process of the flexographic unit, the operator therefore must adjust at least six screw and knob units. This results in the possibility of adjustments being either too great or too little at six different locations, causing the following additional repercussions:
1. Too much ink; PA1 2. Not enough ink; PA1 3. Too much pressure on the plate; PA1 4. Not enough contact with the plate; PA1 5. Squeezing the plates by the intermediate transfer cylinder causing premature plate wear; PA1 6. Squeezing the plate cylinder to the web also causing premature plate wear; PA1 7. There are three points of gear contact which if not adjusted properly, can cause excessive backlash in the gears or the gears will be too tight causing premature gear wear and bad printing.
Furthermore, the slide units for such conventional flexographic printers must be machined and mounted with a high degree of precision machining since the faces of the various cylinders must be held parallel to each other from one side of the unit to the opposite side. The slide units must also have some means of locking to prevent movement and to maintain highly accurate settings.
Accordingly, it is an object of the present invention to simplify flexographic type printing units while increasing the accuracy of adjustability thereof.
It is another object of the present invention to provide a flexographic printing unit in which the ink fountain cylinder is eliminated and in which an ink transfer cylinder is placed in the ink fountain and by means of a simplified doctor blade assembly transfers ink directly from the fountain to the plate cylinder without an intermediate transfer cylinder being used.
A still further object of the present invention is to provide a flexographic printing unit which includes a planetary gear drive unit for changing the registration of the print-to-blank or print-to-print of the plate cylinder as it engages a web.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.